1. Field of Invention
The present invention relates generally to the field of carbon electrode cleaning, and more particularly to the cleaning of spent frame mounted carbon butts following an aluminum smelting process.
2. Technical Background
Aluminum smelting is a chemical reduction process which converts alumina (aluminum oxide) into aluminum and oxygen. The reduction process is typically preformed in a large reduction cell that includes a carbon lined container or "pot" at least partially filled with a molten mixture of alumina dissolved in cryolite and other materials such as fluorides. The carbon lined steel pot forms the cathode while a plurality of frame mounted carbon blocks suspended in the bath form the associated anodes.
During smelting, a voltage potential is applied between the carbon anodes and the pot, resulting in a large current flow from the anodes through the molten bath mixture to the cathode. The electrical current passing through the bath reduces the alumina into its aluminum and oxygen components, which results in the aluminum ions falling from the mixture to the bottom of the pot and oxygen ions reacting with the carbon provided by the carbon blocks to form CO and CO.sub.2. Thus, while aluminum is being formed, the carbon blocks are slowly being consumed over time due to the ongoing chemical reaction of the oxygen with the carbon. Generally, these waste gasses are vented from the pot and the non-suspended aluminum is periodically evacuated from the cell. Over time, this reaction necessitates the replacement of the spent anodes in order to maintain adequate production levels of aluminum.
A by-product of the above-described reaction is the formation of a hardened crust atop the cell. The crust is predominantly formed of cryolite, which over time, begins to accumulate on the carbon blocks and their associated support stubs. Thus, when the anodes are removed from the bath, the remaining carbon remnants or butts supported on the frame of the anodes are substantially covered by a hardened encrustation of cryolite, which until removed, prevents reuse of the remaining carbon butts. Because recycled carbon seasoned by aluminum smelting is preferable to non-seasoned carbon for new or replacement carbon anodes used in aluminum smelting, aluminum manufacturers favor removal of the cryolite encrustation from the spent carbon anodes over disposal of the encrusted anodes as carbon butts can be recycled and reused to make new carbon blocks for later use in the smelting process.
Heretofore, several methods have been employed to remove the cryolite encrustation from the carbon anodes. One such method involves a combination of manually hammering and scrapping the anode to substantially remove the hardened encrustation. Another method employs powered scraping arms, which act upon the cryolite. Still another method employs a vibrating scraping tool. Each of these methods, however, are labor intensive, time consuming, and are generally viewed by the industry as too slow to keep pace with aluminum smelting plants. As many smelting plants typically manufacture their own electrodes as a companion function to smelting, the electrode manufacturing process must keep in step with the smelting process. Accordingly, anode cleaning processes must adhere to strict time guidelines in order to provide the requisite number of cleaned carbon butts desired for new or replacement carbon anode manufacture.
In addition, due to technological advances in reduction cell operation, aluminum smelting plants can now add heavier blankets of alumina to the production cell, which in turn fosters the formation of a thicker and denser crust atop the reduction cell and thus provides for greater heat retention. While this is preferable for increased aluminum output, these advances have resulted in the formation of harder and denser cryolite encrustation formed on the spent anodes.
Accordingly, there is a need for an approved carbon electrode cleaning system and method capable of disengaging these harder cryolite encrustations from the anode frames and carbon butts. More specifically, there is a need for a cleaning system that substantially conforms to the shape of typical carbon butts that remain affixed to the stubs of the anodes so that the encrustation can be removed without additional labor intensive and time consuming manual cleaning operations. Such a device should be simple to use, consistent in operation, and capable of keeping pace with modem smelting and carbon anode reclamation processes preformed at aluminum processing plants. It is to the provision of such a system and method that the present invention is primarily directed.